Plasma lamp with field-concentrating antenna

ABSTRACT

An electrodeless plasma lamp is described comprising a lamp body including a solid dielectric material. The lamp includes a bulb received at least partially within an opening in the solid dielectric material and a radio frequency (RF) feed configured to provide power to the solid dielectric material. A conductive material is provided adjacent to the bulb to concentrate the power proximate the bulb. The conductive material may be located below an upper surface of the solid dielectric material. The conductive material may modify at least a portion of an electric field proximate the bulb so that the portion of the electric field is oriented substantially parallel to an upper surface of the lamp body.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of and claims the benefit of priorityunder 35 U.S.C. §120 to U.S. patent application Ser. No. 12/755,650,filed on Apr. 7, 2010, which is a continuation of and claims the benefitof priority under 35 U.S.C. §120 to U.S. patent application Ser. No.11/619,989, filed on Jan. 4, 2007, and issued as U.S. Pat. No. 7,719,195on May 18, 2010, which claims benefit of priority under 35 U.S.C.§119(e) to U.S. Provisional Application No. 60/756,087, filed on Jan. 4,2006, which applications are incorporated by reference herein in theirentirety.

FIELD

The field of the present invention relates to devices and methods forgenerating light, and more particularly to electrodeless plasma lamps.

BACKGROUND

Electrodeless lamps may be used to provide point-like, bright, whitelight sources. Because electrodes are not used, they may have longeruseful lifetimes than other lamps. Some plasma lamps direct microwaveenergy into an air cavity, with the air cavity enclosing a bulbcontaining a mixture of substances that can ignite, form a plasma, andemit light. However, for many applications, light sources that arebrighter, smaller, less expensive, more reliable, and have longerlifetimes are desired.

Plasma lamps have been proposed that use a dielectric waveguide body toreduce the size of the lamp. An amplifier circuit may be used to providepower to the waveguide body to excite a plasma in a bulb positionedwithin a lamp chamber in the waveguide body.

What is desired are lamps with improved brightness and efficiency whichcan serve as a light source in products such as large-screen televisionsets and digital light processing projection systems. What is alsodesired are improved methods for production of plasma lamps, includingmanufacture of key components and overall lamp assembly.

INCORPORATION BY REFERENCE

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent was specifically and individuallyindicated to be incorporated by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

The novel features of the invention are set forth with particularity inthe appended claims. A better understanding of the present inventionwill be obtained by reference to the following detailed description thatsets forth illustrative embodiments, in which the principles of theinvention are utilized, and the accompanying drawings of which:

FIG. 1 shows a partially exploded perspective view of a plasma lampaccording to an example embodiment including a cylindrical dielectricwaveguide body, a dielectric sleeve insert forming a lamp chamber with alight-reflecting paraboloidal surface, a bulb assembly with a tiplessbulb, and a field-concentrating antenna.

FIG. 2 is an exploded perspective view of the FIG. 1 waveguide body andsleeve.

FIG. 3 is a sectional view of the FIG. 2 waveguide body and sleeve,taken along line 3-3.

FIG. 4 is a sectional view of a one-piece cylindrical dielectricwaveguide body having a lamp chamber with a light-reflectingparaboloidal surface.

FIG. 5 is a sectional view of the FIG. 1 bulb assembly according to anexample embodiment.

FIG. 6 is a sectional view of the FIG. 1 bulb assembly bonded to ametallic holder.

FIG. 7 is a detail perspective view of the FIG. 1 field-concentratingantenna and bulb assembly, and FIG. 6 metallic holder.

FIG. 8 graphically shows the spatial distribution and intensity of theelectric field in the FIG. 1 waveguide body and lamp chamber in theabsence of the field-concentrating antenna, for a resonant frequency of878 MHz.

FIG. 9 graphically shows the spatial distribution and intensity of theelectric field in the FIG. 1 waveguide body and lamp chamber with thefield-concentrating antenna, for a resonant frequency of 878 MHz.

FIG. 10 is a perspective view of a bulb embodiment wherein twofield-concentrating antenna elements are integrated within a quartz bulbassembly.

FIG. 11 schematically shows an electric circuit for a plasma lamp havinga FIG. 10 bulb assembly.

DETAILED DESCRIPTION

While the present invention is open to various modifications andalternative constructions, the embodiments shown in the drawings will bedescribed herein in detail. It is to be understood, however, there is nointention to limit the invention to the particular forms disclosed. Onthe contrary, it is intended that the invention cover all modifications,equivalences and alternative constructions falling within the spirit andscope of the invention as described herein and as expressed in theappended claims.

As shown in FIG. 11, an example embodiment provides a plasma lamp with awaveguide body 132 comprising a dielectric material. In the exampleembodiment of FIG. 11, the waveguide body is configured to resonate whenpower is provided to the waveguide body at a particular frequency. Byoperating at or near a resonant frequency, power builds in the waveguidebody and can be used to ignite and sustain a plasma discharge in a bulb146 adjacent to the waveguide body 132. Electromagnetically, thewaveguide body acts as a resonant cavity in this example. In exampleembodiments, the waveguide body may be configured to resonate in afundamental mode, a second order mode, third order mode or otherresonant mode.

The size of the waveguide body required to achieve resonance at adesired frequency generally scales inversely with the square root of thedielectric constant of the material used. As a result, materials with ahigher dielectric constant may be used to reduce the size of the lamp.In an example embodiment, the waveguide body 132 has a dielectricconstant greater than 1, which is the dielectric constant of air. Forexample, alumina, a ceramic having a dielectric constant of about 9, maybe used. In some embodiments, the dielectric material may have adielectric constant in the range of from 2 to 10 or any range subsumedtherein, or a dielectric constant in the range from 2 to 20 or any rangesubsumed therein, or a dielectric constant in the range from 2 to 100 orany range subsumed therein, or an even higher dielectric constant. Insome embodiments, the waveguide body may include more than one suchdielectric material resulting in an effective dielectric constant forthe body within any of the ranges described above.

In this example embodiment, the waveguide body forms a lamp chamber 140with a tapered wall that reflects light out of the lamp chamber. In someembodiments, the wall may taper to a vertex and form a shape having afocal point in the lamp chamber. For example, the lamp chamber 140 mayhave a paraboloidal or ellipsoidal shape. The walls of the lamp chambermay comprise a reflective dielectric materials (such as alumina) and/orbe coated with a reflective coating such as a thin film, multi-layerdielectric coating. In this example, the reflective surface is not madefrom a conductive material that would prevent or substantially attenuatethe transmission of power from the waveguide body 132 into the lampchamber 140. In one example embodiment, a thin film, multi-layerdielectric coating of multiple layers of silicon dioxide (SiO2) may beused. Another example embodiment uses layers of titanium dioxide (TiO2).Typically, coatings used in the present invention have approximately 10to 100 layers with each layer having a thickness in a range between 0.1micron and 10 microns or any range subsumed therein.

In example embodiments, a bulb 146 is positioned completely or partiallyin the lamp chamber. The bulb contains a fill that forms a plasma andemits light when power is provided from the waveguide body to the bulb.The light is reflected from the walls of the lamp chamber 140 out thefront of the lamp. The position of the bulb and the shape of the lampchamber may be selected to provide a desired ray divergence out thefront of the lamp. In example embodiments, the bulb may be positionedabove the vertex of the lamp chamber such that the arc formed in thebulb is near the focal point of the lamp chamber. In exampleembodiments, the rays exiting the lamp chamber may be convergent,parallel or have some other ray divergence that matches an opticalsystem used with the lamp. For instance, an optical system with lenses,reflectors and/or light pipes may be used in a projection display systemto provide light from the light source to a spatial light modulator(SLM). In an example embodiment, the position of the bulb and the shapeof the lamp chamber may match the ray divergence required by the opticalsystem used with the lamp (e.g., the optical system for a projectiondisplay). The surface shape may be optimized for the desired raydivergence using commercial ray-tracing software, taking into accountthe finite emission volume of the plasma in the bulb, geometricconstraints imposed by the bulb support structure, and constraintsimposed by manufacturing processes. Suitable software products includeZEMAX™, available from Zemax Development Corporation of San Diego,Calif., and CODE-V™, available from Optical Research Associates ofPasadena, Calif. In example embodiments, the lamp chamber may provide areflective surface that approximates a paraboloidal or ellipsoidal shapeand the center of the bulb may be positioned at or near a focal pointfor the particular shape. In example embodiments, the arc length of theplasma is relatively small and the arc may be centered at or near thefocal point of the reflective lamp chamber.

In the example shown in FIG. 11, the bulb 146 may be positionedcompletely inside the lamp chamber 140 and may be at or near a focalpoint of the lamp chamber. In some alternative embodiments, a portion ofthe bulb could be in contact with the walls of the waveguide body oranother material to act as a heatsink. Also, in alternative embodiments,the end of the bulb could extend outside of the lamp chamber to isolateit from the region of highest plasma intensity. However, the exampleembodiment in FIG. 11 uses a bulb positioned completely in the lampchamber and spaced from the reflective walls of the waveguide in orderto provide high brightness and desired reflection/ray divergence. Inexample embodiments, the power is provided along the entire length ofthe bulb, so the arc length of the bulb is determined primarily by thesize of the bulb. The bulb has a relatively short inner length and smallvolume to provide a small arc length and high power density. In exampleembodiments, the arc length may be in the range of from 2 mm to 10 mm orany range subsumed therein. The bulb also has relatively thick walls towithstand exposure to the plasma environment. In an example embodiment,the top and bottom of the bulb have a hemisphere shape with a centralcylindrical section connecting the two ends. In a particular example,the bulb may have an inner width of about 3 mm, an inner length of about5 mm, a volume of about 23.55 mm³ and a wall width of about 3.5 mm.

Other bulb configurations may be used in other embodiments. For example,the bulb may be cylindrical with a planar top and bottom or hemispheretop and bottom; or the bulb may be spherical; or the bulb may have anoval cross section with curved top and bottom surfaces. These shapes areexamples only and other shapes may be used as well such as parabolicallycontoured bulbs or irregularly shaped bulbs (e.g., hourglass shapedbulbs).

Each of the above bulbs has a length L between the inside walls of thebulb and an outer length OL. Each of the bulbs also has a width Wbetween the inside walls of the bulb and an outer width OW. In bulbswith circular cross sections, the width W is equal to the inner diameterof the bulb and the outer width OW is equal to the outer diameter of thebulb. In a spherical bulb, the length and width are both equal to thediameter. For irregular shaped bulbs, the inner width may be determinedby using the largest interior width in the region where power ispredominantly coupled into the bulb and the inner length may bedetermined using the greatest length between distal ends of the bulb.

In example embodiments, the bulb may be in any of the above shapes orother shapes and have, for example, an outer width OW in a range between2 and 35 mm or any range subsumed therein, an inner width W in a rangebetween 1 and 25 mm or any range subsumed therein, a wall thickness in arange between 0.5 and 5 mm or any range subsumed therein, an innerlength L between 3 and 20 mm or any range subsumed therein. In exampleembodiments, the bulb volume may be between 10.47 mm³ and 750 mm³ or anyrange subsumed therein. The above dimensions are examples only and bulbswith other dimensions may also be used in embodiments of the presentinvention.

Example bulbs in any of the above configurations may comprise anenvelope of transmissive material such as quartz, sapphire or othersolid dielectric. In some embodiments, the bulb envelope may be formedfrom a monolithic material. In other embodiments, bulbs may also beformed by a combination of materials forming an envelope. For example, areflective body of ceramic may have an opening covered by a transmissivewindow of quartz, sapphire or other transmissive material. Some bulbsmay also be formed in part by surfaces of the waveguide body and/orother surfaces of a lamp body. For example, a lamp chamber may be formedin the waveguide body and covered by a transmissive window of quartz,sapphire or transmissive material.

Some bulbs may be filled through a small opening that is then sealed.This can form a surface irregularity, called a “tip” or “tubulation”,where the bulb is sealed. In particular, some bulbs may be filledthrough a side wall of the bulb and an irregular side tubulation may beformed. With high temperatures and high pressures in an electrodelessbulb, a side tubulation that is too thin may be susceptible to failureand a side tubulation that is too thick may introduce opticaldistortions. Non-uniformities may also cause localized hot spots thatcan cause failure. For example, the pressure inside an electrodelessplasma bulb may be in the range of from 50 atmospheres to 250atmospheres or more, or any range subsumed therein, and the temperaturemay be greater than 800 degrees Celsius.

In example embodiments, the bulb may be fabricated from a tube ofdielectric material such as quartz using a tipless method that does notform side tubulation irregularities. The tube is sealed at one end and afill is provided through the other end of the tube. The other end of thetube is then closed with a torch at a point about one inch longer thanthe desired inner length. A bulb of this type can be fabricated with arelatively thick, uniform wall to withstand the plasma environment and arelatively small interior volume to confine the plasma arc. Since thesurface irregularities of a tip are avoided, more uniform heatdissipation and more uniform optical surface for light collection may beachieved. In example embodiments, this process may be used to form arelatively thick bulb wall that has a substantially uniform thickness.For example, the wall thickness may be in the range of about 2.5 mm to 5mm or any range subsumed therein and the uniformity of the wallthickness may be within ±5-20% of the wall thickness or any rangesubsumed therein. In some example embodiments, the uniformity of thewall thickness may be within ±0.25 mm.

The bulb may be positioned in the lamp chamber using a pedestal or othersupport. In one example embodiment, a tipless bulb is used and tubingbelow the bulb is retained to act as a support for the bulb. The supportmay be attached to the wall of the lamp chamber or may pass through ahole in the waveguide body and be attached to a separate support. Thebulb may be positioned in the lamp chamber spaced apart from the wall ofthe lamp chamber and below the opening at the top of the lamp chamber.As described above, the bulb may be at or near a focal point for thelamp chamber. In some embodiments, the distance from the interior of thebulb to the bottom of the lamp chamber may range from about half theinner length of the bulb to twice the inner length of the bulb or more.In some example embodiments, this distance may range from 2 mm to 25 mmor more, or any range subsumed therein. In some embodiments, the closestdistance from the interior of the bulb to the walls of the lamp chambermay also be from 2 mm to 25 mm or more, or any range subsumed therein.In some embodiments, the distance from the interior of the bulb to thetop of the lamp chamber may range from about half the inner length ofthe bulb to three times the inner length of the bulb or more. In someexample embodiments, this distance may range from 2 mm to 40 mm or more,or any range subsumed therein. In some embodiments, the focal point andposition of the bulb arc is closer to the bottom vertex of the lampchamber than to the top opening. The above dimensions are examples onlyand bulb configurations with other dimensions may also be used inembodiments of the present invention.

A power source, such as amplifier 138, may be coupled to the waveguidebody to provide power at a frequency in the range of 50 MHz to 30 GHz orany range subsumed therein. The amplifier 138 may be coupled to a driveprobe 134 to provide power to the waveguide body. The drive probe may beinserted into an opening formed in the waveguide body and may be indirect contact with the waveguide body to effectively couple power intothe waveguide body. A feedback probe 136 may be coupled to the waveguidebody and the amplifier to obtain feedback from the waveguide body andprovide it to the amplifier. The feedback probe may be inserted into anopening formed in the waveguide body and may be in direct contact withthe waveguide body to effectively obtain feedback from the waveguidebody.

The outer surfaces of the waveguide body 132 may be coated with aconductive material. In example embodiments, the coating may be metallicelectroplating. In other embodiments, the coating may be silver paint orother metallic paint. The paint may be brushed or sprayed onto thewaveguide body and may be fired or cured at high temperature. In anexample embodiment, the holes where the probes are inserted are notcoated with the conductive coating in order to allow power to beeffectively coupled into the waveguide body and similarly the walls ofthe lamp chamber are not coated to allow power to be coupled from thewaveguide body into the lamp chamber 140. Since the lamp chamber 140 maybe substantially larger than the bulb 146 in order to provide thedesired reflective properties, some embodiments may use conductivematerial adjacent to the bulb to concentrate radio frequency power nearthe bulb. As shown at 142 and 144 in FIG. 11, a conductive material maybe external to the interior of the bulb, but may extend very close tothe interior of the bulb. For example, the material may be about 1 mmfrom the interior of the bulb. In other example embodiments, thisdistance may range from 0.1 mm to 5 mm or any range subsumed therein. Insome embodiments, this distance may be less than the thickness of thebulb wall and the conductive material may extend into the bulb wall. Theconductive material acts as an antenna that concentrates power near thebulb. To avoid arcing and oxidation, the conductive material may beenclosed in a dielectric material such as quartz. In this example, theconductive material may be hermetically sealed in a dielectric material,at least in the region adjacent to the bulb where the power densitiesare the highest. In one example embodiment, the conductive material is athin foil of molybdenum or other conductive material. For example, thefoil may have a thickness of about 100 microns or less. In someembodiments, the foil may have a thickness of about 20 microns or less.A very thin conductive material such as molybdenum foil may beadvantageous, because it can be sealed in a dielectric material such asquartz or even penetrate the bulb wall without causing damage due tothermal expansion of the conductive material inside the dielectricmaterial. The conductive coating on the outer surface of the waveguidebody 132 and the conductive antennas 142 and 144 are grounded. Inexample embodiments, a common ground may be provided for these elements.

In the example embodiment of FIG. 11, the waveguide body is configuredto resonate when power is provided by the amplifier 138 to the driveprobe at a particular frequency. However, the ignition of the plasma inthe bulb and heating of the bulb and the waveguide body may causeresonant conditions to change (for example, due to changes in the loadcharacteristics and thermal expansion of the bulb and waveguide body).The feedback adjusts to changing lamp conditions to sustain oscillation.A phase-shifter PS1 may be used to adjust the phase of the signal aslamp conditions change to reduce reflection of power from the waveguidebody 132 and maintain efficient coupling of power. The phase may also beadjusted during the ignition process to over couple power to thewaveguide body for a short period of time in order to spike the power toexpedite initial ignition of the plasma in the bulb. The phase-shiftermay be controlled by a microcontroller MC1 or other control circuitduring the startup process and steady state operation to achieve desiredoperating characteristics.

Additional details regarding example embodiments will now be describedwith reference to FIGS. 1-10. Referring to FIGS. 1, 2 and 3, a plasmalamp 20 according to an example embodiment includes acylindrically-shaped dielectric waveguide body 22 having a generallycircular outer surface 22S coated with electrically conductive material23, a bore 24 determined by a generally circular surface 24S, andopposed generally parallel upper and lower surfaces 22U, 22L coated withelectrically conductive material 23. A cylindrical dielectric sleeve 30having an outer surface 30S and a paraboloidal lamp chamber 32determined by a surface 32S is closely received within bore 24. Thedielectric sleeve 30 forms the desired reflective lamp chamber 32, butis fabricated as a separate insert that can fit into the bore 24 inwaveguide body 22 for ease of manufacture. While FIGS. 1, 2 and 3illustrate how the dielectric sleeve 30 would be inserted into the bore24, the top of the dielectric sleeve 30 would be aligned with the top ofthe waveguide body 22 when fully assembled in this example embodiment.Waveguide body 22 and sleeve 30 can be made of any low-loss, highdielectric constant material, although alumina is used in a particularexample embodiment.

Plasma lamp 20 further includes a metallic top adapter plate 34 having alower surface 34L to which is electrically grounded an electromagneticfield-concentrating antenna 40, and a metallic bottom adapter plate 36having upper and lower surfaces 36U, 36L. A generally cylindrical,metallic holder 38 having a lip 38L is attached to surface 36U. A bulbassembly 50 having upper and lower ends 50U, 50L is positionedsymmetrically along the common longitudinal axis of waveguide body 22and lamp chamber 32. As described above, the bulb assembly may be formedfrom a tube of dielectric material sealed near one end to form a bulb 56within the bulb assembly. The other end may comprise a length of tubethat supports the bulb assembly. The tube is inserted through holes 25Hand 31H to position the bulb in the lamp chamber 32. Antenna 40 isproximate to but does not touch bulb assembly upper end 50U. Bulbassembly end 50L is closely received within and bonded to holder 38.Surface 36L is attached to a housing 60 including a circuit board 62including a microwave amplifier 63 and associated circuitry, and aheatsink-radiator 64. Adapter plates 34 and 36 are bolted to housing 60.Coaxial feeds leading to drive probe 66 and feedback probe 68 extendthrough circuit board 62 and are received within holes 66H, 68H,respectively, in surface 22L of waveguide body 22. The adapter plateholds the bulb assembly 50 in position relative to the through holes forthe probes and acts as a convenient mechanism for aligning the bulbassembly and probes with the waveguide body 22 and dielectric sleeve 30.Thus, plasma lamp 20 is a single unit integrating the waveguide body 22,lamp chamber 32, antenna 40, bulb assembly 50, circuit board 62, andheatsink-radiator 64.

Still referring to FIG. 3, waveguide body 22 has a lower solid portion25 with a central hole 25H, and sleeve 30 has a lower solid portion 31with a central hole 31H aligned with hole 25H. Bulb assembly 50 isclosely received through holes 25H and 31H. The outer surface 30S ofsleeve 30 is coated with an alumina adhesive 30A which bonds to the boresurface 24S. Chamber surface 32S is coated with a plurality ofmulti-layer dielectric coatings 32C designed to reflect the visiblespectrum, as described above. Although chamber 32 is shown to have theshape of a parabola rotated about the longitudinal axis, its shape canbe any one of a number of similarly rotated conic curves, a plurality ofdiscretely-faceted surfaces, or surfaces of arbitrary shape as optimizedby optical ray-tracing analysis.

Alternatively, a one-piece waveguide body and lamp chamber can be used.FIG. 4 shows a cylindrical, dielectric waveguide body 70 bounded by anouter surface 70S and lower and upper surfaces 70L, 70U. Body 70includes a lamp chamber 72 determined by a paraboloidal surface 72Scoated with a plurality of dielectric coatings 72C. The bottom ofchamber 72 is in communication with a hole 74 sized to closely receive abulb assembly. Holes 76H, 78H are sized to closely receive,respectively, a drive probe and feedback probe.

A plasma bulb must operate at elevated wall temperatures (>800° C.) andinternal pressures (between 50 and 250 atmospheres). Fabrication methodswhich use a separate fill-tube (“tip”) to introduce light-emittingmaterial into a bulb made from tubing stock, may result in a very thinclosure where the fill-tube was attached to the tubing, typically 1-1.5mm in thickness, or other surface irregularities. A bulb with such a“thin spot” may have reliability problems at such high temperatures andpressures and could potentially rupture. Also, using a tip may leave anoptical blemish on the bulb surface which decreases light throughput.Also, thermal asymmetries may develop which can affect consistentevaporation of halides (and therefore consistent color and lumens aswell as consistent warm-up time to full brightness) from bulb to bulb.

In some example lamps, the waveguide body may be narrowed in the regionadjacent to the bulb to limit the length of the plasma region. In theexample embodiments shown in FIGS. 1-4, the bulb is positioned in thelamp chamber spaced apart from the walls to provide desired reflectionand ray divergence. In these example embodiments, the entire internalvolume of the bulb is exposed to power coupled into the lamp chamberfrom the waveguide body. As a result, the length and diameter of theplasma region in the bulb is limited by the dimensions of the bulb andnot the shape of the waveguide body adjacent to the bulb. In order toprovide a short arc, it is desirable to make the interior bulb volumevery short and narrow in the example embodiments of FIGS. 1-4. In oneexample embodiment, the internal length of the bulb may be about 5 mmand the internal width may be about 3 mm.

In some example lamps, the waveguide body may also provide a heatsink toavoid excessive bulb temperatures. In the example embodiments shown inFIGS. 1-4, the bulb is spaced apart from the walls. Without a heatsinkin contact with the bulb, the bulb must survive considerably higherpower loadings per unit surface area (i.e., considerably higher bulbtemperatures). In order to achieve this in the example embodiments ofFIGS. 1-4, the wall of the bulb is made relatively thick with as uniforma wall thickness as practical. A thick-wall bulb will distribute heatfar more uniformly than will a thin-wall bulb, or one with wallthickness irregularities. These properties may be achieved by forming atipless bulb from a tube of dielectric material, such as quartz, inexample embodiments. An additional benefit to fabricating a tipless bulbfrom a tube is a convenient mounting stem formed from the same piece oftubing stock, which can be easily tailored to the desired length tosupport the bulb in the lamp chamber.

An example bulb 56, shown in FIG. 5, is fabricated from tubing stock,such as quartz, without the need for a separate tip. An example methodof fabricating a plasma bulb such as bulb 56 is as follows:

A tube, typically cut from a piece of longer stock, is selected havingan outer diameter and wall thickness about the same as those of thedesired bulb, and a length that depends on the desired length of thebulb assembly. In one example, the outer diameter is about 7 mm and thewall thickness is about 2 mm.

The tube is cleansed and rinsed.

Using a hydrogen-oxygen torch, one end of the tube is rounded andsmoothed on a glass-lathe to form an approximately hemispherical closure(52, FIG. 5) with an inner radius about the same as the tube innerradius, and a wall thickness about the same as the tube wall thickness.In other embodiments, other heat sources or mechanisms may be used toclose the end of the tube.

The partially formed body is re-cleansed.

The open end (54, FIG. 5) of the tube is filled with a “light-emitter”.Typically, mercury or indium bromide is used. Other light-emittersubstances may be used in other embodiments, including iodides, bromidesand/or chlorides of lithium, sodium, potassium, rubidium, cesium,strontium, scandium, cerium, praseodymium, neodymium, gadolinium,dysprosium, holmium, hafnium, thallium, lutetium, yttrium, erbium,thulium, terbium and europium. Pure metals and halogens can also beintroduced into the tube to achieve desired properties.

The filled tube is attached on a high vacuum system with a standardfitting of the appropriate diameter (e.g., an UltraTorr™ fittingavailable commercially from SwageLok Inc.) and evacuated. The tube isthen backfilled with the desired “starting gas” at the desired pressure.Typically, the starting gas is argon, although neon, krypton or xenonmay be used in other embodiments. In example embodiments, the gaspressure is in a range between about 10 and 500 Torr or any rangesubsumed therein.

The tube is then closed with a hydrogen-oxygen torch at a point (55,FIG. 5) approximately one inch longer than the desired inner length(about 5 mm) of the bulb, to form a bulb (56, FIG. 5). The sealed bulbmay be frozen in the tube using a cryogenic material such as a liquidnitrogen bath, so the stem can be heat collapsed at negative pressure upto the desired bulb edge without evaporation of the internal fillmaterials creating internal positive pressure.

The bulb and attached stem (58, FIG. 5) are removed from the vacuumsystem. If necessary, the stem can be trimmed to the correct length.Residual silica dust is removed from the lamp surfaces usinghydrofluoric acid or buffing compound.

The bulb assembly may be mounted to a structure exterior to thedielectric waveguide body, such as adapter plate 36 in FIG. 1. The stemacts as a bulb support and extends through holes 25H and 31H as shown inFIG. 3 to position the bulb 56 at the desired location in the lampchamber 32. This provides an easy way to secure and align the bulb andposition it in the lamp chamber. In alternate embodiments, a bulbsupport may be bonded to the bottom of the lamp chamber or the waveguidebody with a sintered alumina-powder layer or other adhesive material tohold the bulb in the desired position.

FIG. 6 shows the stem 58 mounted within holder 38 and bonded to theholder with high temperature, epoxy cement. Holder 38 includes a screw39 for attachment to bottom adapter plate 36. The overall length of thebulb and stem is dependent on the desired position for the bulb in thelamp chamber. In example embodiments, this may depend upon the focallength of the lamp chamber's reflecting surface and details of themounting design.

In example embodiments, the dielectric waveguide body 22 has one or moreresonant modes each manifested as a certain spatial-intensitydistribution of radio frequency (RF) field confined within the body. Asuitably designed antenna within the lamp can intercept the RF field inthe lamp chamber to create AC currents therein. The AC current in theantenna can in turn radiate into a partially enclosed space in which thebulb is closely received. The dimensions of this space must be smallcompared to the RF field wavelength; the net effect is a concentrationof RF field in the enclosed space, i.e., space proximate to the bulb. Aconductive material adjacent to the bulb may be used to form an antennaof this type and thereby concentrate the RF field near the bulb.

Referring to FIG. 7, field-concentrating antenna 40 is a “top” antennahaving a wire cage 42 forming a tight semi-enclosed space around bulb 56at a separation in a range from about 0.1 mm to 5.0 mm or any rangesubsumed therein. Cage 42 is attached to a rigid lead-wire 44 whichmaintains the position of cage 42 and forms a common electrical groundwith coatings 23, adapter plates 34, 36, and housing 60. In exampleembodiments, such antennas may be fabricated from a conductor with ahigh melting point having an electrical conductivity greater than 10⁷Siemens/meter. Example embodiments may use conductive materials such asnickel, platinum, molybdenum and titanium. In addition to machining,antennas can be fabricated using stamped sheet-metal or even wire. Inexample embodiments, the antenna thickness is selected so that it isthick enough to resist melting, and thin enough to avoid blocking anunacceptable fraction of light. Also, in example embodiments, theantenna thickness is selected to be significantly larger than the RFpenetration depth (“skin depth”). In example embodiments, thethicknesses may be in the range of from about 0.1 to 2 mm or any rangesubsumed therein. In example embodiments, the antenna is grounded to aconductively-coated surface of the dielectric waveguide body. Variousphysical shapes for the antenna can be used to achieve these properties.A top antenna, bottom antenna, or both can be used. In exampleembodiments, the enclosure can take the form of a wire cage, fork orring. Other shapes can also be used in other embodiments. The shapes ofa top and bottom antenna can be different in some embodiments. Design ofsuch antennas can be optimized using commercial electromagnetic modelingsoftware such as HFSS™, available from Ansoft, Inc. of Pittsburgh, Pa.,and FEMLAB™, available from COMSOL, Inc. of Burlington, Mass. In theseexample embodiments, the field-concentrating antenna is not physicallyconnected to the drive or feedback probe.

FIG. 8 shows a design simulation, using the HFSS™ software package, ofthe electric field spatial-intensity distribution in a cylindricalalumina waveguide body 80 resonating at a frequency of 878 MHz. Body 80includes a paraboloidal lamp chamber 82 into which is inserted a bulbassembly 84 with a bulb 86, and contains an inserted drive probe 88. Forsimplicity, the feedback probe is not simulated because its coupling tothe field (and hence its perturbation on the field) is small by design.The arrows point in the direction of the electric field; their lengthsindicate relative intensity. FIG. 9 shows the electric fieldspatial-intensity distribution when a cage 92 of a field-concentratingantenna 90 forms a tight semi-enclosed space around bulb 86 at aseparation of 1 mm. The field-concentrating effect of antenna 90 isevident. Such simulations predict that the ratio of field strength inthe center of a bulb with and without an antenna is in a range fromabout 1.05 to 10.

FIG. 10 shows an example bulb assembly 100 having a “top-and-bottom”antenna configuration. In this example embodiment, the antennas areenclosed in a dielectric material, such as quartz tubing extending fromthe top and bottom of the bulb. This helps avoid problems that can leadto failure of a bare antenna. A bare antenna may have failure mechanismsdue to arcing to a conducting surface, and/or rapid oxidation or meltingdue to high RF currents flowing through the antenna(s) and/or hightemperature conducted or radiated from the bulb. Bulb assembly 100,which is fabricated from quartz tubing, includes a central bulb 102disposed between upper and lower stems 104, 106. Opposed “top” and“bottom” antenna elements 108, 110 are spot-welded, respectively, tolead-wires 112, 114 which exit the bulb through tubing openings 116,118, respectively. Antenna elements 108, 110 are connected to a commonelectrical ground. At each bulb assembly end, multiple lead-wires may beused to improve both electrical and thermal conductivity. Antennaelements 108, 110 are sealed in a dielectric material, such as quartz,and lead-wires 112, 114 are fixed in position when the bulb 102 isformed by sealing the tubing at locations 119A, 119B. Lower stem 106 isclosely received within and bonded to metallic holder 120 which includesa screw 122 for attachment to bottom adapter plate 36. Antenna elementsmay be strips of molybdenum micro-foil typically having a thickness ofabout 0.001 inch, and a length in a range of 2 to 10 mm, or any rangesubsumed therein, and a width in a range of 1 to 5 mm, or any rangesubsumed therein. The use of very thin foils and spot-welding preventscracking of the quartz-enclosing seals as well as failure due toexpansion mismatch of any diameter of metal wire capable of conductingthe RF currents to which the antennas are exposed in the hightemperature environment. The simple geometry of a bulb assembly such asassembly 100 makes it easier to fabricate than a bulb assembly such asassembly 50. The above antenna configurations and dimensions areexamples only and other configurations may be used in other embodiments.

A bulb assembly such as bulb assembly 100 can be fabricated eitheraccording to the “one-piece” method described above for bulb assembly50, or by presealing the antenna elements in separate stems which arethen fused to the bulb. The following summarizes example bulb assemblyfabrication processes for both one- and two-stem/antenna configurations:

A finished bulb assembly can be produced with a single stem (forattachment to a dielectric waveguide body and/or lamp chamber by cementor other means), or with a stem at each end for enclosing andpositioning an antenna at either end or both ends. As described above,in example embodiments, the antenna may be a molybdenum micro-foil inclose proximity to the bulb, with outer conducting wire(s) spot-weldedto the micro-foil and attached to an electrical ground. If there is tobe a sealed antenna at the upper end, that antenna may be hermeticallysealed into the upper stem using a “shrink” seal process. This is doneby presealing in a separate stem, later to be fused to a partial bulbassembly including the bulb with the open lower stem already attached,but before the fill material(s) are inserted and before a secondantenna, if used, is sealed into the lower stem. Alternatively, theupper antenna can be sealed into one arm of a preformed assembly with anopen stem on each end using a shrink seal process. The bulb assembly(with the upper stem heremetically sealed and attached if an upperantenna is to be used; otherwise without an upper arm, but with the bulbassembly sealed everywhere except for an open lower stem) is then filledunder clean conditions through the lower stem with the required solidand/or liquid fill material(s). If an antenna sub-assembly (e.g, theantenna element and lead-wire(s)) in the stem is to be mounted in thedielectric waveguide body or lamp chamber, the antenna with the attachedlead-wire(s) are then inserted into the lower stem and aligned intoaxial position. The bulb assembly is then placed at an appropriatestation for filling the lower stem and bulb with rare gas. The fillmaterial(s) and all parts of the antenna sub-assembly are completelyenclosed in the bulb/lower stem and the bulb assembly is attached to thegas-filling apparatus by an 0-ring or other suitable means. After(negative gauge pressure) gas-filling, the lower stem is “long-tipped”(i.e., collapsed by heating at a distance beyond the inserted length ofthe foil/lead-wire(s) sub-assembly). The hermetically sealed structureis then placed in an apparatus which immerses the bulb assembly into acryogenic environment (e.g., liquid nitrogen) so that final sealing ofthe lower stem (with or without the antenna sub-assembly) can beaccomplished by heat collapsing the stem at negative pressure up to thebulb edge without evaporation of the fill material(s) creating positivepressure (which would prevent collapsing of the quartz under appliedheat and final closure). Each bulb assembly stem is then cut to anappropriate length, exposing the lead-wire(s) for attachment to thecommon electrical ground. A metal (or, if lead-wires protrude, a slottedmetal or non-conducting end cap) can be attached to the lower stem ifneeded for precise alignment of the bulb.

1. An electrodeless plasma lamp comprising: a lamp body comprising asolid dielectric material; a bulb received at least partially within anopening in the solid dielectric material; a radio frequency (RF) feedconfigured to provide power to the solid dielectric material; and aconductive material adjacent to the bulb to concentrate the powerproximate the bulb.